Mary Gates, one of Seattle's most prominent civic figures and the mother of Microsoft magnate Bill Gates, died at her Laurelhurst home early this morning after a months-long bout with breast cancer. She was 64.

Years before her son gained international prominence, Mrs. Gates was widely respected as a tireless community-service advocate, a prominent role model for women seeking corporate advancement, and a skilled behind-the-scenes negotiator. But when it came to accepting credit, she was careful to deflect the spotlight away from herself and onto her many causes.

"Mary is the perfect example of being able to get a whole lot done if you don't worry about who gets the credit," said the Rev. Dale Turner, a longtime family friend, in an interview earlier this year.

The granddaughter of a prominent Seattle banker and civic figure, J.W. Maxwell, Mrs. Gates liked to describe herself as "a Seattleite through and through." She was proudest of her 18 years as a University of Washington regent. But she was at least as well-known for having opened doors of corporate boardrooms and executive suites to women during the 1970s.

"There were very few women involved in government affairs, and I was determined to change that," said former Gov. Dan Evans in an interview earlier this year. Evans, a onetime bridge partner, named Mrs. Gates as a regent in 1975, only to succeed her on the board last year. He said Mrs. Gates had "broad community

She was to be honored today by the Municipal League of King County as Citizen of the Year for her long career and successes in community service. In a press release on its annual awards luncheon, the League cited Mrs. Gates' efforts as a "judicious, exceptionally talented civic-minded citizen."

Last night, the UW Alumni Association honored Mrs. Gates with its annual recognition award. Her husband and three children attended the ceremony on the UW campus and accepted the award in her behalf.

Born in then-rural North Seattle in 1929, Mrs. Gates attended Bryant Elementary and Roosevelt High schools. She enrolled in the University of Washington, graduating in 1950 with thoughts of a teaching career. After marrying Bremerton assistant city attorney Bill Gates Jr., whom she had met as a law student at the UW, she taught junior high school in Bremerton and at Seattle's Jane Addams before the birth of daughter Kristianne in 1954.

After son Bill, born in 1955, and daughter Libby, in 1964, completed her family, Mrs. Gates turned to volunteerism with the Junior League, Children's Orthopedic Hospital and United Way.

In 1975, the year her son co-founded Microsoft, Mrs. Gates became the first woman president of United Way of King County, the first woman director of First Interstate Bank of Washington, and only the fifth woman regent. In 1983 she was named the first woman to chair the national United Way's executive committee.

Thoughtful and questioning in the Socratic method, Mrs. Gates was a steadying influence on the regents board during turbulent times. When the university's South African investments drew protest in the early 1980s, Mrs. Gates pushed first for adoption of the Sullivan human-rights principles and later for divestiture. She also steered the regent's fiscally strategic Metropolitan Tract Committee, in charge of the university's 11-acre property downtown, through critical lease negotiations during major building renovations in the 1980s.

Mrs. Gates was "a source of balance, wisdom and stability on the regents - its center of gravity," said UW President William Gerberding, in a recent interview.

Mrs. Gates also figured in her son's success. She helped cement Microsoft's early connection with IBM, which led to development of the IBM PC with DOS, an operating system supplied by Microsoft. When someone mentioned Microsoft to IBM President John Opel in 1980, Opel responded, "Oh, that's run by Bill Gates, Mary Gates' son." Opel served with Mrs. Gates on United Way's national board at the time.

Mrs. Gates was recalled as a gracious hostess by early Microsoft executives on visits to her Laurelhurst home after the company moved to Bellevue from Albuquerque in 1979. Later the Gates clan, under her stewardship, sponsored annual Microgames, Olympics-like summer competitions drawing local community leaders, software-industry executives and Microsoft employees to the family compound on Hood Canal.

The mother-son connection clicked in luring nationally known bioengineer Lee Hood to the UW from Caltech two years ago. The Microsoft magnate contributed $12 million to UW biotech research. And Mrs. Gates nudged her usually apolitical son to fight state budget Initiatives 601 and 602 last fall.

Throughout her career, Mrs. Gates promoted philanthropic causes. After the death of Ned Skinner in 1988, she took over Washington Gives, the civic volunteer project that urges people to donate 5 percent of their income and 5 hours a week of their time.

In 1991 the Gateses were named philanthropic family of the year by Washington Gives.

Mrs. Gates also helped launch Leadership Tomorrow, the future executives and entrepreneurs program, and served on the boards of Unigard Security, US West, Seattle Symphony, KIRO and the Children's Hospital Foundation.

Mrs. Gates is survived by her husband, Bill, a senior partner with the law firm of Preston Gates & Ellis; three children, Kristianne Blake of Spokane, Libby Armintrout and Bill, both of Seattle, and four grandchildren.

A memorial service will be at 4 p.m. next Thursday at University Congregational Church in Seattle.

The family has suggested remembrances be sent to the United Way Endowment Fund, 107 Cherry St., Seattle 98104-2223; or Cancer Lifeline, Suite 680, 1191 Second Ave., Seattle 98101.